Antenna mount



A. B. BAILEY ANTENNA MOUNT June 14, 1960 2 Sheets-Sheet 1 Filed June 16. 1955 FIG.

FIG.

INVENTOIR flF/VOAD B BA/LEY ATTORNEY-5 June 14, 1966 4 Filed June 16, 1955 FIG. 6.

AZL

A. B. BAILEY ANTENNA MOUNT FIG. IO.

2 Sheets-Sheet 2 'I'IIIIIIIIIII'IIIIIIII FIG. 9.

7'1 x1? 9% 5: & 7a 6 i as INVENTOR ARA/04D 5. 54/45) ATTORN EY5 ANTENNA MOUNT Arnold B. Bailey, Francestown, N.H ('41 Thoreau'sn, Concord, Mass.)

Filed June 16, 1955, SELNO- 515,805

'3 Claims. (Cl. 343-713) This invention relates to an improved antenna mount and particularly of a type for supporting and feeding endsupported and voltage-fed vertical antennas intended for mobile service, such as on automobiles or boats.

The mounting of an antenna on an automobile for mobile radio transmitting and/ or receiving presents a number of difficult problems. To begin with, the antenna and its support must be able to withstand severe bending and vibration forces-such as the wind or high speed movement of the automobile. If the diameter of the antenna, for example, is at all substantial, the force of the wind blowing against it may be enough tobreak-it loose from its supporting structure, .or. at leastto set. lip-dangerous whipping and lashingibackand forth.

A mobiletransmitterhasneed for an antenna which is not only strong but which is able to radiatea signal to a given destinationdependably even-thoughthe antenna is frequently beingmoved by the vehicle upon which itis mounted to different environments. Each move to a newplace; of course, affects the radiation characteristics of' the antenna. A half-wave antenna supported" a suitable? distance above-the ground plane has been found-to be noticeably better for this purpose than a quarter-wave'antenna. The better performance of the former overthe latter. for such applicationmakes it desirable. to. find some efficient means not heretofore available for mounting it andv coupling it to theradio equipment.

It is conventional to mount a quarter-wave antenna projecting upward: from the. roof: of an: automobile, providedof coursezthat. thereof: is metal. Though a'halfwave antenna could 'be' similarly. mounted,it becomes difficult to avoid. excessive: base capacity effects which lead to :low electrical efiiciency. Furthermore, such an antenna cannotbe directly connected to conventional transmission lines. Thisis particularly truefof ahalfwave antenna'intended for operation at a frequency of 100 megacycles-or higher;

A big. drawback with mounting a vertical half-wave antenna directly on the bumperfof a car'is the distortion in-theantennaradiation pattern caused by the nearby metal'surfacesof th'ecar. Added to this is the fact that when the bottom end ofthe antenna is mounted level'with the bumper,:ne'arby objects,-such as other 'carsor" fire plugs, mailrboxes'and'the like have more effect on the radiationpatternthan if the antennawere mounted with its bottom end somewhat above the bumper level.

The only half-wave antenna, so far as is known,-which performs well'electrically when mounted on ashort post or the like'extendingup from and elevating the antenna above a car bumper or other-similar-ground plane, is that shownin-US. Patent- No. 2,184,729. This antenna, commonly known asa coaxial antenna, isone-half wavelengthlong and can :bemounted. on a post-like support a short distance above a ground plane without. adversely affecting the radiation pattern of the antenna. The postlike support, if properly dimensioned will not radiate. However, although this type Of antenna is electrically suitable for use with mobile equipment, informs as described nitcd States Patent ice 2 and shown in said patent it is physically unsuitable "for that purpose because of the large diameter of the jsleeve which extends over the lower half of its active length. Such a sleeve, as mentioned previously, is' greatly affected by wind and vibration and is therefore not practical for use on a mobile base, as an automobile or small boat.

Accordingly, an object of this invention is to improve the radiation characteristics of half-wave, end-fed, vertical dipole antennas supported above structures onwhich they are mounted; v,

to provide a strong, compact, and very efficient coupling arrangement to match such antennas to low'impedance lines; and I to provide an eflicient coupling arrangementwhich is small, compact and rugged enough for mountingvertical half-wave antennas on automobiles and the like The present invention provides a new'structure for supporting and feeding a half-wave antenna of small outside uniform diameter so that it can be mounted easily and securely in the most advantageous position above a car bumper, or the like, and so that the half wave antenna will not be adversely affected by the support and-will thereby radiate and receive efficiently; In accordance with one aspectof the invention, a mount for this purpose includes a coupling element or'unit for end-feeding a thin rod-like half-wave antenna; This unit which is 'also of small size is connected electrically so as to provideoptimum matching between the relatively high impedance of the antenna and the low' impedance of the usualtransmission line. Thus, the antenna can bemounted on said'unit at certain elevated 'positionsabo've the ground planewithout there being radiation from the support which holds the antenna provided -that the sup'port'is 'of' suitable dimensions. Since-"the antenna itself is of th'efutino'st simplicity and verysm'all in diameter along its' entire length, and since the coupling" unit issm'alhand of light weight, they are physically well suited for nifobile use. In addition, the electricalperformance of this light'and easily transportable equipment, as employed withautomobiles and boats, for'exainple, exceeds that of 'con'veiitional types of subs'tantiallyheavier; more complex and cumbersomecoaxial antennas.

A fuller'understanding of theinvention and itsadvantages'and use's will'be gained from the follo'win'g' de'scription of embodiments thereof illustrated inthe accompanying drawings in which.

Figure 1 is a view in elevation of an antenna'system embodying the invention in a form suitable for being mounted on'an automobile;

FigureZ is a central verticalsection'on enlarged scale through one form of inductive loading coupling unit that connects the radiating portion of the antennato the'supporting base as shown in Figure 1;

Figure 3 is a fragmentary view in elevation on enlarged scale showing a form'of coupling unit including means for adjusting its impedance transformation fcha'ract'e'r istics;

Figure 4 is a fragmentary view partly in central longitudinal section of a couplingunit similarto that of Figure 2 and showing a modification in the basbonn'ectiofis to and supportfor the coupling unit;

Figure 5 is a view in elevation of a modification in which the antenna is a multi-element Yagi type; 1 p,

Figure 6 shows a Yagi antenna similar to that of-Figure 5 except that the supporting post therefor is hollow and encloses a portion of the coaxial feed line;

Figure 7 shows-a plurality of co-operatingsYagi antennas arranged with one superimposed on another and adjustable into and out of a common vertical plane;

Figure 8 showsa modification wherein two horizontally polarized Yagi antennas-are mounted on a single post;

tudinal section, of a modified form of coupling unit wherein the loading is dielectric;

Figure is a similar view of a portion of an antenna structure embodying a coupling unitwherein the loading is magnetic and the supporting post serves also as part of a coaxial feed line; and

Figure 10A is a fragmentary view on enlarged scale showing details of construction of the device of Figure 10, more particularly the solder connection between an upper end portion of the outer element of the feed line and the inner surface of the supporting post.

Referring to Figure l, the radio-energy radiating and receiving portion or antenna of the antenna assembly is shown as a vertical metal rod or tube 2 of such length as to provide the desired characteristics and pattern of radiation, in this example, approximately one-half wavelength long at the frequency of operation. Rod 2 can be aluminum or other suitable material of small diameter along its length.

The automobile bumper 4 acts as the ground point for the conductive supporting structure of the antenna 2 which for reasons stated previously, is supported in operative position a short distance above bumper 4. This antenna supporting structure includes a post 6 and a coupling unit 8 mounted thereon. Post 6 includes a springtype or other resilient connection Ill with an internal shorting strap for eliminating the inductive effect of the spring. Spring 10 is conveniently positioned to absorb shock and to permit yielding resistance to forces applied laterally to the antenna or to portions of themount locatedabove connection 10. a

The coupling unit 8 provides both a secure mechanical support for. the antenna rod 2 and also an effective impedance matching element to couple energy between said rod 2 and the low impedance feed supply line, as the coaxial cable12.

As seen in Figure 2, unit 8 includes an outer shield or shell conveniently in the form of a metal tube or sleeve 4 a receiver, the same antenna structure being usable both for receiving and for transmitting. The upper or open end of tube 18 is protected by a cap 34 of a suitable weatherproof insulating material which serves also to hold the lower end of rod 2 and core 22 in a proper or predetermined relation to the tube. Cap 34 can be permanently'fixed around rod 2 and removably fastened to the tube by screws 36 or alternatively cap 34 may provide a tight resilient weatherproof fit for rod 2 and yet allow rod 2 to be removed through it when desired. Such construction permits rod 2 to be removed easily and quickly from unit 8 so that if desired a differ- 7 ent antenna can be' inserted therein as will be explained 18 having one end closed by a metal wall 19. Unit 8 is secured to the upper end of post 6 by a screw 20 extending through an opening in bottom wall 19 and threaded into a cylindrical core 22 within tube 18, the latter, for example, being made of copper. The core 22 may be formed of phenolic base plastic, high-strength polystyrene,

fibre, impregnated wood, or other material that will not absorb excessive moisture and will not introduce excessive losses at the frequency of operation. Said core 22 is arranged in tube 18 with its upper end supporting the lower end portion of rod 2 which is secured in the upper end of core 22 by means of the screw 26.

Unit 8 also serves to couple energy between coaxial cable 12 and rod 2. Where the loading is of the induction type, a coil, as a strip of sheet or braided copper, or other suitable material, is extended in a helical coil 28 conveniently of three to six turns around core 22 1 from one end to the other. The upper end of coil 28 is connected conductively to the lower end of rod 2 through,

for example, a circular metal bushing 30 between the upper end of core 22 and the lower end of rod 2 and to which the upper end of coil 28 is soldered at point 31.

. This arrangement also provides a capacitance connection between said coil 28 and rod 2 which results automatically by reason of what is known in the art as stray capacity supplied by and implicit in the relative positions and conditions of said coil and rod.in operation.

The upper end of the conductive outside sheath 13 of the coaxial cable 12 is soldered to bottom wall 19 at 29 The inner conductor 14 of said cable passes through an opening 32 in wall 19 and is connected to coil 28 a suitnection between the upper end of conductor 14 and coil 28 is selected to provide the best match between the impedance of cable 12 and that of antenna rod 2. Coaxial 1 or toanother source of radio frequency energy, or to able distance above point 29. The exact place of conhereinafter.

Unit 8 is in efiecta transformer either self-resonant by itself or resonant in conjunction with the antenna at the selected frequency of operation. A coupling or transformer of this short length is made possible by the electrical loading, as for example the inductive type using the coiled strip 28 withintube 18, or other suitable types later referred to. Where the electrical length of unit 8 together with its support 6, grounded at its lower end as shown, is less than a quarter wave-length, for example 5 wave-lengthor less, their aggregate outside surface will not support a substantial amount of radiation at the frequency of operation. Accordingly, since unit 8 and post 6 can be made effectively non-radiating by maintaining their aggregate outside surface at optimum value, the bottom of antenna 2, Figure l, or the antenna 52, Figure 6, for example, can be supported above the ground 'point or plane as bumper 4, without adversely affecting the pattern of radiation or reception. If a greater height above the ground plane is desired or necessary, support 6 can be lengthened, without impairing the radiation characteristics of the assembly as a whole, by an integral multiple of a half wave-length, thus producing a total physical length of unit 8 and support 6 within substantially A L of the length according to the formula: L=)\/2(N) where a is an electrical wave-length measured on the outside surfaces of unit 8 and post 6 and N is an integer. The coupling unit shown in Figure 2 does not provide for adjustment of the transformation ratio once set. However,

in case it is desired to replace antenna 2 with one having a substantially difierent impedance, it is advantageous to have some means of adjusting unit 8 to match the new impedance.

Figure 3 shows a modification of unit 8 wherein the point of connection of conductor 14 to coil 28 can be varied. Here, the top end of conductor 14 is connected to a conductive portion of a sliding brush assembly 40 which can 'be pushed along the helical slot 41 cut through the wall of tube 18 along a line coincident in level with at least a part of the turns of coil 28. An inner contact 44 carried by assembly 40 presses against coil 28 and connects conductor 14 to it at a point determined by the position of'assernbly 40 along slot 41. Assembly 40 includes an insulating bushing 46 having shoulders mating with the walls of slot 41 and which can be tightened thereagainst as desired by means of the screw 48.

Figure 4 shows a modification of the structure shown in Figure 2. Here, supporting post 6 is made integral with the resonance chamber or tube 18; and the bottom and is electrically connected to coil 28 at its lower end.

The characteristic impedance of unit 8 is made the geometric mean of the impedance of line 12 and the antenna rod 2. i

Figure ishows a vertically polarizedYag antenna Two xdirectorelements 58 and 60,

ment. The dimensions of the directors 58 and 60 and the reflector 62 are selected in accordance with usual design practice for Yagir'a-ntennas. In the illustrated emhodiment, radiating element 54 is electrically one-half wave-lengthlong at the mid-portion of the operative frequency band for the installation. The support for this antenna'is similar'tothat previously described, except thatan additional mechanical brace 65, suitablyinsulated from the'antenna,extendsbetweenpost 6 and the body of the automobile.

Attimes it may be desirable to substitute a directional antenna, asa rotatably-mounted Yagi antenna52, for

'anon-directional'one,as antenna rod 2, or-vice-versa,

and an advantage of the'present invention is that this may readily beadone. -In the event, for example, that the antennarod 2 and Yagi 52-have-the same or substantially the same frequency of operation, the two can be interchanged. These can be interchanged without adjustment of the transformer characteristics of unit 8 in the event the antenna impedances are equal or approximately equal. Rod 2 is removed simply by unscrewing the screws 36 and the end of rod 2 from core 22, and Yagi 52, with a cap 34 attached to the lower end of radiation element 54 thereof, is mounted on unit 8 by securing the inner end of said element in the upper end of core 22 and tightening the screws 36 of cap 34 or alternatively, removing antenna 2 alone by unscrewing at thread 26, and screwing. in Yagi 52.

Figure 6 shows another arrangement for supporting and feeding a Yagi antenna similar to that shown in Figure 5. In this example, the antenna is supported on a hollow post or pipe 6, which is in turn mounted on a suitable base, as a tripod 68, thus permitting the coaxial cable 12 to enter pipe 6 at its bottom open end so that the presence of the cable thus shielded does not interfere with the radiation characteristics of antenna 52. The coupling unit 8 may he one of any of the types herein described.

Figure 7 shows an assembly of three Yagi antennas, 52, 52a and 52b, arranged one above another and energized by a coaxial cable 12 extending through tubular post 6, as in Figure 6, to a coupling unit 8. A single vertical rod mounted in the end of coupling unit 8 provides the radiating or driven elements 54, 54a and 54b of the antennas 52, 52a and 52b respectively, and also the connecting conductor portions, as 55, between elements 54 and 54a, and 55a between elements 54a and 54b. Each of conductor portions 55 and 55a is one-half wavelength (or any odd multiple thereof) long and each has a tubular shielding sleeve, as 70, which coaxially encloses conductor portion 55 in spaced relation thereto, and 70a which similarly encloses conductor portion 55a. Antennas 52, 52a and 52b can be oriented in the same vertical plane if maximum directivity and gain is desired. Alternatively, each can be oriented in a difierent vertical plane if wider or specialized directivity is preferred. The impedance of these three antennas together is onethird that of each. Thus by stacking an appropriate number of such antennas in the way shown, it is possible to obtain a composite antenna having a relatively low impedance.

An advantage of supporting and end-feeding the radiating element of Yagi antennas is that the arrangement of feed line 12, coupling unit 8 and support 6, as in Fig- {11138 S'throirghfli for example;-whenthecombined-length of :saidesupport and unit:is:ldetermiued.- according. to .the previouslyngiven formula, does. not adversely atfect 1 the radiation :patterns of these antennas. However, 1 where the'radiating element corresponding to element 5420f a verticalYagia antenna is center fed, asin conventional-arrangements; the :unavoidable presence .ofthevertical .portion oftthexfee'd 'linesand its supporting :pole inzthat relation to the antenna assembly causes dist-unbancesi-nzthe radiation 'pattern.

Figure .8 shows .arsystemrfor separately rend-feeding two horizontally polarized radiating elements @of .Yagi

antennas 52L and 52R suppo'rtedon a single mount. In

this example, both ot the coaxial cables 12L sand 12R extend upwardly through t-he supporting lpipe 6, done leading into-coupling unit 8L and the other into the ooupling-unit-ZSR. 'These couplirrgunits aremounted' with their longitudinal axes "positioned horizontally -and extend outwardly frcrn the supporting post-6 in opposite direc tions, each i being connected at its innerJend to one of the cables and at its outer end being connected to and supported one post 6. -A' continuationof post 6 extends upward through core 74 and upon emerging therefrom becomes the antenna rod 2. Shield 76 has a bottom wall 78 which is electrically connected to post 6 and to which the outer conductor 13 of the cable 12 is connected. The inner conductor 14 of this cable passes through an opening in Wall 78 and connects to the continuation of post 6 within core 74 at the appropriate point for impedance matching. Where antenna 2 is made integral with post 6, an exceptionally strong antenna assembly structure is obtained.

Figure 10 shows another antenna assembly structure including a coupling unit 82 similar in some respects to that shown in Figure 9, but with dilferent base connections and wherein magnetic loading is used. In this example, the cable 12 extends upwardly within supporting pipe 6 a suitable distance into the core 84 and then the outer end of its inner conductor 14 turns through an opening in the continuation of post 6 and passes laterally through the core and into contact with the inside of the surrounding conductive sleeve 86. The location of this point of contact is selected to provide the desired impedance matching characteristics of the unit. The upper end of outer conductor 13 of cable 12 is soldered at 13a, Figure 10A inside post 6 near the opening through which conductor 14 passes. Core 84 is made of a suitable insulating material, such as polyethylene, through which is dispersed a finely divided magnetic material such as a normal ferrite core material. The over-all length of the coupling unit 82 is, as in the case of previously described couplers, less than A Wave-length. The radiating portion 2 of the antenna is one-half wave-length long; and the upper end of coupling unit 82 is positioned above the ground plane 88 according to the previously stated formula.

It is contemplated that various changes or modifications in the embodiments shown and above described can be made by those skilled in the art without departing from the spirit or scope of the invention as set forth.

I claim:

1. An arrangement for supporting and for end-feeding an antenna, said arrangement comprising an antenna element which is substantially a half wave length long, means defining a ground plane, and coupling and supporting means for holding said element with its longitudinal axis generally perpendicular and with its lower end spaced from said plane, said coupling and supporting means including a resonant transformer coupled to the )7 lower end of said antenna element and-adapted to apply voltage thereto at an impedance substantially matched to that of said element, the outside surface of said coupling and supporting means being conductive and having a length above said ground plane such that said surface is non-resonant at the frequencyof operation whereby the radiation characteristic of said antenna is not adversely affected by the presence of said coupling and supporting means.

2. The combination of elements as in claim 1 in which said antenna is part of a vertically polarized Yagi antenna.

3. An antenna mount assembly comprising in combination a vertical half wave antenna element having an eifective radiating extent of one half wave length at operating frequency, means defining a ground plane, a coaxial low impedance energy supply cable having a conductive sheath enclosing a conductor wire electrically connected to energize said antenna element, and a non-radiating means for supporting said antenna element including a tubular sleeve supported above the ground plane and having a conductive lateral wall and a conductive closing wall at its lower end and being open at its upper end and having an effective radiating extent of less than one quarter of a wave length at operating frequency, a conductor mounted coaxially within and spaced from lateral interior wall surfaces of said sleeve, one end of said conductor being electrically connected to said sleeve and its other end being electrically connected with said antenna element, and-said conductor also being electrically connected to said conductor wire of said coaxial cable, and

References Cited in the file of this patent UNITED STATES PATENTS 1,745,342 Yagi Ian. 28, 1930 2,113,136 Hansell et al. Apr. 5, 1938 2,124,424 Leeds July 19, 1938 2,275,342 Brown Mar. 3, 1942 2,431,124 Kees et a1. Nov. 18, 1947 2,485,177 Wehner Oct. 18, 1949 2,492,404 Streib et al. Dec. 27, 1949 2,725,473 Darling Nov. 29, 1955 2,750,589 Harris June 12, 1956 FOREIGN PATENTS 535,055 Great Britain Mar. 27, 1941 592,763 Great Britain Sept. 29, 1947 

